to each other (a plane above the plane), thus forming sandwich-like structures (H-
aggregates).
In accordance with this, it can be assumed that when an ion-associative bond is
formed, at least some of the dye ions are located close enough to each other, most likely
in neighboring positively charged units of the polymer. Thus, the electrostatic binding
of the dye anions with a polymer promotes their π-π dispersion interaction. H
aggregates are formed as can be judged by the hypsochromic shift of the dye absorption
band.
Figure 12. Interaction of polyelectrolyte CPAT and Bromphenol Blue:
a) Absorption spectra of Phenol Red in the presence of polyelectrolytes CPAT
with different charge density.
1 – CPAT 5%; 2 – CPAT 10%; 3 – CPAT 30%; 4 – CPAT 55%; 5 – CPAT 70%; 6 – CPAT
95%; C
PE
= 12 mg
L-
1, pH 3.6, C
Dye
= 20 μmol L
-1
, l = 1 cm;
b) Dependence of ΔA on solution pH in the presence of polyelectrolytes CPAT.
ΔA – difference between absorbances of solutions with and without polyelectrolyte.
C
CPAT
= 12 mg L
-1
, C
PE
= 12 mg L
-1
, C
Dye
= 20 μmol L
-1
, λ = 592 nm, l = 1 cm
Confirmation of the proposed mechanism of interaction between BPB and the
investigated polyelectrolyte was obtained by studying the spectra obtained for a series
of polymers differing in charge density (Fig. 12a).
For polymers with a charge density of 5 and 10%, the band of the aggregated dye
is absent in the spectrum. At the same time, with an increase in the charge density up
to 95%, the band at 570 nm appears and its intensity proportionately increases. As the
charge density increases, the fraction of positively charged polymer units increases,
which statistically turn out to be adjacent to each other. In accordance with this,
probability is growing that the dye ions will be in the neighborhood, thus, favoring the
aggregation process.
When studying the dependence of the formation of IA between BPB and CPAT,
a region was found on the curve of ΔA versus pH in which there were differences
a
b
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